Weather & Hybrid Characteristics – Their Roles in Grain Corn Dry Down

Updated from Crop Chatter Posts Made in 2012 and 2015

Grain corn in Manitoba is maturing quickly, and some of the earliest maturing fields have reached physiological maturity. Normal plant processes and weather conditions are the major influences on grain dry down, although hybrid characteristics can also play a role. As corn harvest approaches, a quick review of the facts concerning grain drydown might be helpful.

Grain drydown can be separated into two stages: the grain fill period and after physiological maturity.

Drydown During Grain Fill. The grain fill stages (R1 to R5) begins at flowering and is completed at physiological maturity. Grain filling is characterized by the rapid accumulation of dry matter in the kernel and the rapid movement of water out of the kernel.  Decreases in kernel moisture occur from a combination of actual water loss (evaporation) from the kernel surface and the accumulation of dry matter.  The corn plant uses “internal plumbing” to move water out of the kernel since water movement out of the kernel is regulated by how much dry matter is being forced into the kernel.  The corn plant is much more efficient in removing water from the kernel using its “internal plumbing” instead of physical evaporation through the kernel surface.

Drydown After Physiological Maturity. Physiological maturity (R6) occurs when kernel moisture is at approximately 30% (but can vary).  At this stage of growth, a layer of cells at the base of the kernel dies and turns black (hence black layer), the “internal plumbing” is therefore disconnected, and a barrier is formed between the kernel and the corn plant.  For this reason, post-maturity grain moisture loss occurs primarily by evaporative loss from the kernel itself. Research many years ago established that post-maturity moisture loss through the kernel connective tissues (placental tissues) back to the cob is essentially non-existent.

Role of Weather. As moisture loss after maturity is due to physical evaporation, field drying of mature corn grain is influenced primarily by weather factors, especially temperature and humidity.  In simple terms, warmer temperatures and lower humidity encourage rapid field drying of corn grain.

Because moisture loss is greatest just after physiological maturity, both because the weather is usually warmer and because wet kernels lose water more easily, it stands to reason that a corn crop that matures earlier in the season will dry down faster than a crop that matures later in the season.  However, it is important to keep in mind that grain moisture loss for any particular day may be quite high or low depending on the exact temperature, humidity, sunshine, or rain conditions that day. It is not unheard of for grain moisture to decline more than one percentage point per day for a period of days when conditions are warm, sunny and dry. By the same token, there may be zero dry down on cool, rainy days.

Role of Hybrid Characteristics.  A number of hybrid characteristics can influence the rate of dry down, but to a lesser degree than weather. However, when weather conditions are not favorable for rapid grain dry down, hybrid characteristics that influence the rate of grain drying become more important.  The relative importance of each trait varies throughout the duration of the field dry down process and, as mentioned earlier, is most influential when weather conditions are not conducive for rapid grain drying.

  • Husk Leaf Number. The fewer the number of husk leaves, the more rapid the grain moisture loss.
  • Husk Leaf Thickness. The thinner the husk leaves, the more rapid the grain moisture loss.
  • Husk Leaf Senescence. The sooner the husk leaves senesce (die), the more rapid the grain moisture loss.
  • Husk Coverage of the Ear. The less the husk covers the tip of the ear, the more rapid the grain moisture loss.
  • Husk Tightness. The looser the husk covers the ear, the more rapid the grain moisture loss.
  • Ear Declination. The sooner the ears drop from an upright position to a downward position, the more rapid the grain moisture loss.
  • Cob Diameter. The narrower the cob diameter, the more rapid the grain moisture loss.
  • Kernel Type.  Flint-dent kernel types tend to dry down slower in comparison to dent kernel types due to the harder nature of the kernel.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Manitoba Agriculture on Twitter: @MBGovAg
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Manitoba Agriculture website: www.manitoba.ca/agriculture
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Corn Cobs in Tassels – What is the Cause?

Updated from a Crop Chatter post made August 2012

In talking with Morgan Cott, Agronomist with the Manitoba Corn Growers Association, producers are reporting seeing corn cobs in the tassel of plants. Although relatively uncommon, this phenomenon called ‘tassel-ear’ is reported almost every year.  A tassel-ear is very noticeable in the field and is often found on tillers of a corn plant along the edges of a field or in areas of low plant populations. Although it is uncommon to find tassel-ears that develop on the main stalk of a corn plant, it can happen.

Tassel Ear (P.de Rocquigny, 2015)

Tassel-Ear in Corn (Photo by P. de Rocquigny, 2015)

So How Do Tassel Ears Happen? A corn plant has a monoecious flowering habit where the plant has both male and female flowers.  What many may not know is that both flowers are initially bisexual.  During the course of development the female components (gynoecia) of the male flowers and the male components (stamens) of the female flowers abort, resulting in tassel (male) and ear (female) development.

Now every once in a while, the upper flower that typically becomes a tassel instead forms a combination of male and female floral parts on the same reproductive structure. The physiological basis for the survival of the female floral parts on the tassel is likely hormonal, but the environmental “trigger” that alters the hormonal balance is not known.

It has been noted that can be varietal differences where different hybrids produce ears in the tassel and is linked to a particular set of genetics. Ear development in the tassel may also occur when the plant sustains hail or mechanical damage early in its development.  Pollen shed would not have been affected, nor will yields be decreased as a result of this phenomenon.

Submitted by Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

For more information on the production and management of corn, please visit Manitoba Agriculture’s website at:  http://www.gov.mb.ca/agriculture/crops/specialcrops/bii01s01.html

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Why am I seeing Tillers in my Corn?

I have been receiving a few calls over the season regarding tillering in corn. So I figured a Crop Chatter post based on an article I wrote back in 2005 would be good to answer some questions. Is it only due to plant populations? What could be other causes? What effect will tillering have on crop growth and yield potential?

What are Tillers? And What Causes Them?  Tillers are lateral branches that form at below ground nodes. Although tiller buds form at each below ground node, the number of tillers that develop is determined by plant population and spacing, soil fertility, early season growing conditions, and the genetic background of the hybrid.

  • Plant Population: Many hybrids will take advantage of available soil nutrients and moisture by forming one or more tillers where stands are thin in the row or at the ends of rows. However, excessive tillering may indicate problems with stand density and distribution. If tillering is associated with row gaps and less than optimal plant populations, these are the conditions which need to be corrected to ensure optimal yields.
  • Soil Fertility: Tillers are most likely to develop when soil fertility and moisture supplies are ample during the first few weeks of the growing season. They are usually visible by the 6-leaf stage of development.
  • Genetics: Hybrids with a strong tillering trait may form one or more tillers on every plant even at relatively high populations if the environment is favorable early in the growing season. If a particular hybrid shows excellent yield potential and also produces extensive tillering under some growing conditions, it should not be avoided.
  • Weather Conditions: Hail, frost, and flooding injury that destroy or damage the growing point early in the growing season can also result in tiller development and non-productive plants.

What is the Effect on Yield Potential? When farmers see extensive tillering in their corn hybrids, they often express concern that the tillering will have a detrimental effect of crop performance (that the tillers will “suck” nutrients from the main plant and thereby reduce yields). As a result, tillers are often referred to a “suckers”. However, research has shown that tillers usually have little influence on grain yields and what effects they do have are generally beneficial. Recent studies have found that there is little movement of plant sugars between the main plant and tillers before tasselling.

After silking and during grain fill, substantial amounts of plant sugars may move from earless tillers to ears on the main plant. When there are ears on both the tiller (often called ‘tassel-ears’) and the main plant, little movement of plant sugars occurs. The main plant and tillers act independently, each receiving sugars from their own leaves. The ‘tassel-ears’ that tillers may produce, therefore have no impact on the ear development of the main plant as was once thought and don’t contribute to yield.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
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Estimating Date of Grain Corn Maturity from Silking Stage

The 2015 season has seen relatively normal accumulation of corn heat units (CHU), with a range of 92% of normal to upwards of 111% of normal as of July 19th. According to Issue #12 of the Manitoba Crop Report, grain corn ranges in development from late vegetative stages to silking (R1).

Silking marks the start of the reproductive phase of development and begins when the silk becomes visible outside the husk and pollination occurs. Each silk is attached to an ovule which will become a kernel if pollinated. The CHU accumulation from planting to silking is about 50 to 55% of that required for the plant to go from planting to physiological maturity.

While this could be used as a general guideline, temperature and relative maturity of the hybrid must be taken into consideration. Plus, the duration of each stage during grain fill can also be influenced by soil fertility, cultural practices (plant populations), and moisture.

If we consider CHU accumulation and maturity rating of the hybrid, we can calculate the number of corn heat units required for a crop to pass from silking to physiological maturity. As mentioned above, the period from planting to silking takes approximately 50 to 55% of the total heat units required for the crop. Therefore, the remaining 45 to 50% would be needed to carry the crop from silking to physiological maturity. The table below identifies the approximate CHU requirements to bring a corn crop from silking to physiological maturity based on a range of CHU maturity ratings.

Table 1: Approximate Corn Heat Unit (CHU) Requirements from Silking to Physiological Maturity for Various Hybrid Maturities.

CHU Rating of the Hybrid Approximate CHU Required from Silking to Physiological Maturity
2100 945 to 1050
2200 990 to 1100
2300 1035 to 1150
2400 1080 to 1200
2500 1125 to 1250
2600 1170 to 1300

 

Once a crop’s CHU requirement from silking to physiological maturity is determined, the next step is to establish the number of CHU that can reasonably be expected from the date of silking until the end of the season.  Referring to Tables 2 and 3 (where dates of expected additional CHU accumulation from two silking dates in the season), we can estimate the approximate date when a given accumulation of CHU past silking is reached.

For example, if the silking stage of a 2200 CHU hybrid grown near Morden occurred around July 18, the crop would require approximately 990 to 1100 CHU to go from silking to physiological maturity (see Table 1 and use 1100 for simplicity).  According to Table 2, the accumulation of 1100 CHU starting July 18 would occur by approximately September 5 in Morden.  It is important to keep in mind that these numbers are estimates based on historical observations.  Some years will have temperatures above or below average, causing the dates to shift forward or back.

Table 2: Date of Expected CHU Additional Accumulation from July 18 at Various Manitoba Locations (Source: Environment Canada averages 1971-2000).

From July 18 +900 +1000 +1100 +1200 +1300
Brandon 31-Aug 07-Sep 14-Sep 25-Sep 10-Oct
Elm Creek 28-Aug 03-Sep 09-Sep 17-Sep 27-Sep
Emerson 26-Aug 31-Aug 06-Sep 12-Sep 19-Sep
Morden 26-Aug 30-Aug 05-Sep 10-Sep 17-Sep
Portage 28-Aug 03-Sep 09-Sep 17-Sep 28-Sep
Selkirk 26-Aug 31-Aug 06-Sep 12-Sep 21-Sep
Starbuck 29-Aug 04-Sep 10-Sep 17-Sep 28-Sep
Steinbach 28-Aug 03-Sep 09-Sep 16-Sep 26-Sep

 

Table 3: Date of Expected CHU Additional Accumulation from July 25 at Various Manitoba Locations (Source: Environment Canada averages 1971-2000).

From July 25 +900 +1000 +1100 +1200 +1300
Brandon 12-Sep 22-Sep 05-Oct 01-Oct
Elm Creek 08-Sep 15-Sep 25-Sep 08-Oct
Emerson 05-Sep 11-Sep 18-Sep 28-Sep 12-Oct
Morden 04-Sep 10-Sep 17-Sep 26-Sep 09-Oct
Portage 08-Sep 16-Sep 26-Sep 12-Oct
Selkirk 05-Sep 12-Sep 20-Sep 01-Oct 24-Oct
Starbuck 08-Sep 16-Sep 25-Sep 09-Oct
Steinbach 08-Sep 15-Sep 24-Sep 08-Oct

 

Remember that this is only estimating time from silking to physiological maturity, not when harvest can start.  Field dry down rate from physiological maturity to start of harvest is influenced primarily by weather factors and, to a lesser degree, by hybrid characteristics.  In simple terms, warmer temperatures and lower humidity encourage rapid field drying of corn grain.  Because moisture loss is greatest just after physiological maturity, both because the weather is usually warmer and because wet kernels lose water more easily, it stands to reason that a corn crop that matures earlier in the season will dry down faster than a crop that matures later in the season.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

For more information on corn production, please visit MAFRD’s webpage at http://www.gov.mb.ca/agriculture/crops/production/grain-corn/index.html
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How to Determine Leaf Stage in Corn

Knowing what leaf stage your corn crop is at is extremely important since post emergent herbicides can only be applied to corn up to the label-specified leaf stage. Therefore both farmers and agronomists need to accurately stage corn plants. Herbicide labels often refer to plant height, crop growth stage (leaves or collars), or both when discussing corn growth stage limits for the application of postemergence herbicides. Below is a review of some common methods for determining growth stage. It is important to know which method the herbicide manufacturer is using to indicate correct herbicide application timing. For each method, the stage of the corn plant in Figure 1 will be determined.

Corn Plant Staging

Figure 1: Corn Plant Staging

 

Corn Height Method.  To determine corn plant height, measure from the soil surface to the highest point of the arch of the uppermost leaf whose tip is pointing down.  Don’t measure to the “highest point” on the plant, which is often the tip of the next emerging leaf above.  Refer to Figure 1 on how to correctly determine the height of a corn plant.

Both environmental and management conditions can have a great impact on the height of a corn plant. In cool, wet springs, corn often grows more slowly from a height standpoint but it is still advancing physiologically. A delayed seeding date, differences in tillage, and differences in soil type can also have a pronounced effect on plant height but relatively little effect on the stage of vegetative development. Hybrid can also have an effect on plant height as shorter-season hybrids tend to produce shorter plants. Because corn height varies a great deal due to growing and crop management conditions, it is not the most accurate way to stage corn plants.

Leaf Over Method.  The leaf over method is a common way of measuring leaf number. The leaf over method counts the number of leaves, starting from the lowest one (the coleoptile leaf which has a rounded tip) up to the last leaf that is arched over (tip is pointing down). Do not count leaves younger (inside) than this one, even though they are present in the whorl. In Figure 1, the corn plant would be at the 4 leaf stage.

Leaf Collar Method (V-stage).  The leaf collar method is generally the easiest to use. It also relates better to the physiological stage of the plant and thus to the effects of herbicides. Staging by the leaf collar method is done by counting the number of leaves with visible collars, beginning with the lowermost, short, rounded-tip true leaf and ending with the uppermost leaf with a visible leaf collar . Collars are not visible until the leaves are developed enough to emerge from the whorl. In Figure 1, the corn plant would be at 3 leaf stage (V3).

Staging Corn with Severe Leaf Damage.  Dead leaf tissue will not resurrect itself and will eventually slough off as the plants continue to grow. The question is whether the leaf stage of a recovered plant begins anew with the healthy leaves or whether the dead leaves (which may no longer be visible) should be counted. In other words, should a 3-leaf plant that has lost 2 leaves to frost injury now be considered a 1-leaf plant?

The simple answer is: If corn was a 3-leaf plant prior to the frost, physiologically it still is a 3-leaf corn plant after the frost, no matter how many lower leaves are damaged, dead, or otherwise missing.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

For additional information on how a corn plant develops, please visit MAFRD’s website at http://www.gov.mb.ca/agriculture/crops/production/grain-corn/how-a-corn-plant-grows.html
For the Guide to Crop Protection:  http://www.gov.mb.ca/agriculture/crops/guides-and-publications/index.html#gfcp
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Over Wintering Corn? Points to Consider

There remains grain corn to be harvested in some parts of Manitoba, due in some cases to high kernel moisture contents and immature crop.  Corn in the field may dry about 0.3 to 0.5 percentage points per day during October; however, that decreases to 0.15 per day or less during November.  The amount of drying in the field will depend on factors such as corn maturity, hybrid, moisture content, air temperature, relative humidity, solar radiation and wind speed.

Table 1: “Estimated” Corn Field Drying

Picture3Source:  Dr. Kenneth Hellevang, NDSU Extension Service.

 

However, what is interesting is regardless of kernel moisture content in November, if left standing the crop can dry down moisture contents below 20%.  The following figure from MASC illustrates this point.

Figure 1:  Grain Corn Moisture Content Change (1992)

Picture2

Source: MASC

 

Yield Loss.  If the stalks stay standing and there isn’t much ear drop, snow cover or wildlife damage, the crop can get through the winter without much yield loss. However, notice the number of disclaimers in that sentence. Ear drop will vary by hybrid and environmental conditions as well as the amount of grain on the ear (smaller ears should stay attached better than larger ears).  Stalk strength may have also been compromised this year due that early September frost event; although the cool temperatures did not kill the plant outright and only leaf material, the plant would have ‘scavenged’ resources from within itself, i.e. the stalk, to help with grain fill.  This would lead to compromised stalk strength.

If winter conditions are cool without snow then corn will continue to dry and can be harvested throughout the winter.

If you do find yourself in the position of wanting to over winter your corn, please touch base with your local MASC agent.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

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Determining Final Plant Stands in Corn

The corn crop in Manitoba is now planted and corn is emerging quickly!  Over the next few weeks is when producers should be evaluating their final plant stands as plants emerge and develop through early leaf stages.

Did You Hit Your Plant Stand Target or Miss it? 

To determine plant population or stand, count the number of corn plants in a row length equal to 1/1000 acre. Multiply that number by 1000 to get the number of plants per acre.  Do this several times in a field to get a representative sample.

  • In a 30-inch row spacing, count the plants in a 17’4″ row.
  • 20-inch row spacing, count the plants in a 26’1″ row.
  • 22-inch row spacing, count the plants in a 23’8″ row.

Now compare the final plant populations achieved to what you intended to plant, i.e. calculate your attrition losses.  If losses range up to 10% or more, investigate the reasons.  Was germination impacted by cold, wet soils? Did insects like wireworms or cutworms impact final plant stands?  Identifying the cause(s) behind the losses is important.  It can help determine whether changes in your planting operation or agronomic decisions may improve the odds of good stand establishment in the future.

Also keep in mind that corn that initially emerges and develops uniformly through early leaf stages can take a turn for the worse around the three- to four-leaf stage if the plant is damaged by insect or disease prior to the successful development of nodal roots from the crown area of the plant.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist

 

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Should you plant corn after canola?

Planting corn after canola can result in corn being impacted by phosphorus deficiency, or what is commonly called “corn after canola syndrome”.  Phosphorus enters the corn plant through root hairs, root tips, and the outermost layers of root cells.  Beneficial fungi, called mycorrhizae, enhance P uptake in corn early in the season because the mycorrhizae strands increase the effective rooting volume of plants.  This is extremely important for uptake of immobile nutrients, such as P.

In corn, up to 80% of early season P uptake is by mycorrhizae since the strand network may extend 8-12 inches from root.  Crucifer plants, such as canola, sugarbeets, and mustard, are not hosts for mycorrhizae so the mycorrhizae must regrow from spores.  This is why early in the growing season you might see corn suffering from P deficiency.

Although the mycorrhizae eventually regrow and colonize the roots, the damage done by lack of P early in the growing season may have already occurred.  Yield may be impacted by the early season P deficiency, maturity of the crop may be delayed and grain moisture content at harvest may be higher (leading to higher drying costs).

How Common is Grain Corn Planted After Canola in Manitoba?

In Yield Manitoba 2014, Anastasia Kubinec (Provincial Oilseed Crops Specialist) updated her crop rotation tables based on information MASC contract holders provide to MASC.  These tables provide trends that can be used to help with crop rotation choices.  If we dig into the data from the 2008 to 2012 time period, 22% of the grain corn acres were planted into canola stubble.  In fact, it was the most popular choice for producers, followed by planting corn into soybeans (16%) and into spring wheat (10%).  So the data illustrates there are other factors producers look at when planning their grain corn crop rotations, and not necessarily the influence of beneficial fungi.

What is the potential impact to yield?

The same data source provides details on the yield response of those rotations (see Table 1 below).  Grain corn  yields are lower following canola than soybeans or spring wheat.

Table 1: Relative Yield Response (per cent of 2008-2012 average) of Manitoba crops sown on previous crops (stubble >120 acres)

Previous   Crop  Crop   Planted – Grain Corn 
Hard Red Spring Wheat 100
Winter Wheat 87
Barley 99
Oat 93
Canola 95
Soybean 103
Sunflower 99
Grain Corn 87
Yield (bu/ac)  95

The initial phosphorus uptake can be an issue but is this practice manageable?

To avoid ‘corn after canola syndrome’, producers should grow a crop less dependent on mycorrhizae for P uptake after canola (corn & flax are two of the most dependent crops).

If rotation requires corn after canola, a “Plan B” is to supply high starter P levels to try and overcome any P deficiency problems that might occur.

Variable results are seen with in-crop treatments to remedy phosphorous deficiency.   If products are tried, it is recommended to leave a check strip to determine effectiveness on crop recovery and yield.

For more information, please see the complete article by Anastasia in Yield Manitoba 2014 at: http://www.mmpp.com/mmpp.nsf/ym_2014_06_crop_rotation_tables.pdf.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist

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Why is there a cob in my corn plant tassel?

Although relatively uncommon, this phenomenon is reported almost every year.  As most know, a corn plant has a monoecious flowering habit where the plant has both male and female flowers.  What many may not know is that both flowers are initially bisexual.  During the course of development the female components (gynoecia) of the male flowers and the male components (stamens) of the female flowers abort, resulting in tassel (male) and ear (female) development.

Now every once in a while, the upper flower that typically becomes a tassel instead forms a combination of male and female floral parts on the same reproductive structure. The physiological basis for the survival of the female floral parts on the tassel is likely hormonal, but the environmental “trigger” that alters the hormonal balance is not known.

It has been noted that can be varietal differences where different hybrids produce ears in the tassel and is linked to a particular set of genetics. Ear development in the tassel may also occur when the plant sustains hail or mechanical damage early in its development.  Pollen shed would not have been affected, nor will yields be decreased as a result of this phenomenon.

For more information on the production and management of corn, please visit Manitoba Agriculture’s website at:  http://www.gov.mb.ca/agriculture/crops/specialcrops/bii01s01.html

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